1. Field of the Invention
The present invention relates to a composition for a photo-alignment film, a photo-alignment film and a method for producing the same, a liquid crystal cell, and a liquid crystal display that have an excellent resistance to light etc., and allow imparting alignment controllability for liquid crystal molecules with a small light irradiation dose.
2. Description of the Related Art
Methods for aligning liquid crystals have been used for producing alignment films and the like for liquid crystal displays.
As the methods for aligning liquid crystals, known are methods for chemically or physically treating the surfaces of supports, and among these, well known is a rubbing method, in which the surface of a support is coated with a polymeric resin film of polyimide or the like to be an alignment film, and the alignment film is unilaterally rubbed with cloth or the like. The rubbing method allows obtaining a homogeneous alignment of liquid crystals aligned parallel to the surface of a support as well as unilaterally and uniformly.
However, the rubbing method has problems in that static electricity and dust are generated by rubbing of the alignment film to lower the yield and that it is difficult to quantitatively perform alignment control.
A photo-alignment film process has gained attention as a method that can solve the problems of the rubbing method, in which a photo-alignment film to be imparted with liquid crystal alignment controllability is imparted by irradiation of light is provided on the surface of a support, and the photo-alignment film is irradiated with light to align liquid crystals. As the photo-alignment film process, there is, for example, a report on a technique for using, in the form of a photo-alignment film, a compound, such as an azobenzene derivative, that causes an isomerization reaction through the action of light (see Japanese Patent (JP-B) No. 2990270).
However, the technique described in JP-B No. 2990270 has had such a problem that liquid crystal alignment controllability deteriorates in the course of exposure of the photo-alignment film to light because of a low light resistance of the photo-alignment film, and the production cost is high because a large irradiation dose of light is necessary for causing an isomerization reaction.
There is also a report on, as the photo-alignment film process, a technique for using a composition for a photo-alignment film containing an azo monomer and an amino resin for production of a photo-alignment film (see Japanese Patent Application Laid-Open (JP-A) No. 2007-121721). The technique described in JP-A No. 2007-121721 (Patent Document 2) allows producing a photo-alignment film excellent in resistance with a small light irradiation dose. However, even by the technique described in JP-A No. 2007-121721, reduction in the light irradiation dose is still insufficient, and a photo-alignment film that can be produced with a low irradiation dose of light from the standpoint of production cost etc., while an excellent resistance is maintained has been demanded.
Accordingly, a satisfactory photo-alignment film and a satisfactory method for producing the same that have an excellent resistance to light etc., and allow imparting alignment controllability for liquid crystal molecules with a small light irradiation dose have not yet been provided under the present circumstances.